1. Field of the Invention
The present invention related generally to cathodic arc plasma physical vapor deposition processes, and more particularly to multiple layer formation processes.
2. Description of the Prior Art
The present invention basically comprises a combination of electrostatic powder coating techniques with cathodic arc plasma physical vapor deposition techniques, and has particular application to the coating of cast articles of manufacture composed of metal, plastic or other materials. Cast articles of manufacture typically have many voids and pits in the outer surface of the cast article, and it is desirable to remove or eliminate these voids and pits. Utilizing the prior art electrostatic powder coating process, an electrically charged powder coating is applied to an electrically grounded, cleaned cast article of manufacture. In this process, an electrostatic spray gun is utilized to spray a diffused cloud of electrically charged powder particles onto the grounded article. Following the powder layer application, the article is mounted into an oven to cure the powder layer. A typical curing process involves heating the powder coated article to a temperature of approximately 350.degree. Fahrenheit for approximately 15-20 minutes. During the curing process the powder material melts and hopefully flows into the surface voids and pits to fill them. The melted outer surface of the powder layer thus becomes smooth. Following cooling and removal of the article from the oven, the article now has a smooth outer surface instead of the cast surface with its voids and pits. The cured powder layer also acts as a corrosion resisting layer on the outer surface of the article.
Typically, the prior art cured powder coating layer is relatively soft and lacking in aesthetic appeal. Therefore, an outer layer has been applied to the powder coated article, and the utilization of a cathodic arc plasma physical layer deposition process is known. In this outer layer deposition process, the article having a cured underlayer is mounted within the chamber of a PVD device and a vacuum atmosphere is created. Thereafter, the cathodic arc is struck and an outer layer is deposited upon the article. Typical outer layers consist of metal or metal compounds such as chromium, ZrN and TiN. Following deposition of the outer layer, the article is cooled and then removed from the PVD chamber. A high gloss, scratch resistant outer surface is provided to the article of manufacture, whereby a two layer overall coating process is completed.
A first problem with this two layer prior art process is that air bubbles sometimes become trapped in the voids and pits during the powder layer curing step. Following completion of the curing step the outer surface of the cured powder layer is smooth, however, the trapped air bubbles remain. Thereafter, when the article is placed within the PVD chamber and the vacuum is created, the air bubbles expand and often explode through the surface of the cured undercoat layer, thus creating pits and craters in the outer surface. The subsequent deposition of the PVD layer does not fully fill these pits and craters, whereupon a marred outer surface is obtained. A second problem with the prior art process, as compared to the present invention which is described herebelow, is that the prior art process unnecessarily utilizes energy and time in the oven mounting and curing process steps. As is next described, the present invention eliminates the oven mounting and curing process.